Our goal is to explore the three-dimensional architecture of cells and tissues using the high voltage electron microscope (HVEM) and computer methods for image processing. We will improve the Boulder HVEM by fitting it with a high tilt eucentric stage and a low light level television system. We will buy an image processing computer to improve the information available to the microscopist as he adjusts the microscope for picture-taking. The same computer will also be used to construct three dimensional representations of biological structures both from serially tilted image of one structure and from serial sections. We will build a device to minimize the dose of electrons used for imaging a specimen, and install a tilting cold stage. Through collaboration, we will experiment with the usefulness of tomographic methods for 3-dimensional reconstruction of biological specimens. We plan 3 core programs in fields of biology where the proven power of high voltage electron microscopy to provide high resolution images of thick specimens will be of significant importance: one on the cytoskeleton, one on neurobiology, and one on chromatin and nuclear structure. In each subject area, scientific questions are posed whose answers will be significant in their own right, but whose answering will require the development of new approaches and technologies for specimen preparation, electron imaging, and image interpretation. Numerous collaborative projects are described which will take advantage of the particular characteristics of HVEM. Many of these projects will also profit from the technical developments planned in core research. We will continue and expand a service by which potential users of our installation can mail specimens for our staff to examine. Our training activities will include an annual workshop in the use of the HVEM and the completion and circulation of a pamphlet on HVEM techniques. We will also initiate a program for "HVEM Scholars" who will come to Boulder to attend the workshop and then continue through the summer on a project of their own. For dissemination we will complete a flier describing our installation and continue to describe the uses of the HVEM in publications and symposium talks. We also plan bi-annual conferences on biological subjects suitable for study with the HVEM.